1. Field of the Invention
This invention relates to the use of special combinations of polyurethane-urea-forming starting components which provide for the solvent-free processing of components that are liquid at room temperature, show very rapid gelation, are cold-hardening and are eminently suitable for corrosion-inhibiting, wear-resistant coatings applied by casting, centrifugal casting or spraying by means of multicomponent metering units onto large, even vertical metal surfaces and moldings and for lining the interior of tubes and also for the elastic coating of plastics, foams and natural stone and of screed surfaces or concrete.
The components are liquid, relatively low-viscosity mixtures of polymer-containing or polyadduct-containing polypropylene oxide polyols and/or ethylene oxide-containing polypropylene oxide polyols containing special, low-melting, readily soluble aromatic diamines and tertiary amine catalysts as component (A) which are reacted at room temperature with liquid polyisocyanates based on diphenyl methane diisocyanate or based on their NCO-prepolymers with polyether polyols as component (B).
2. Description of the Prior Art
Casting and spraying processes for components forming polyurethane elastomers are known per se, the components also being metered, optionally intermittently by high-pressure delivery units. Processes of this type are described in Vieweg/Hochtlen, KunststoffHandbuch, Vol. VII, Polyurethane, Carl Hanser Verlag, 1966, on pages 121 to 134, 135 to 205 (for foams) and 206 to 247 (specifically for elastomers). Although polyurethanes may be firmly applied to metals by the processes in question, shrinkage problems frequently arise (pages 211-212). One special method of processing glycol-extended elastomers is the spraying process in which for example all the components are simultaneously mixed and sprayed in the same operation. To this end, a few percent of highly active catalysts, such as tin(IV)dibutyl dilaurate or tin(II)octoate, generally have to be added. Unfortunately, these large quantities of tin catalysts lead to elastomers that are sensitive to aging. Where polyethers are used, more favorable elastomer properties are obtained with aromatic diamines as chain extending agents than with diols, although in this case, too, higher temperatures are required for melting, transporting and metering the components and also for after-heating in molds (pages 224 to 228). In the case of spraying processes for coating vertical surfaces, relatively large quantities of very highly active tin catalysts have to be used to prevent the components from running (cf. pages 242 to 244).
DE-A No. 2,928,182 describes cast elastomer systems which show improved processibility through the use of diisocyanate isomer mixtures of from 15 to 80 mole percent of 2,4'-, from 20 to 85 mole percent of 4,4'- and from 0 to 20 mole percent of 2,2'-diisocyanato diphenyl methanes. To this end, an NCO-prepolymer of 1 mole of a relatively high molecular weight dihydroxy or polyhydroxy compound having a molecular weight of from 400 to 10,000 and from 2 to 10 moles of the diisocyanato diphenyl methane isomer mixtures is reacted with an aromatic diamine or, optionally, mixtures thereof with at most 50 mole percent of a polyol containing primary hydroxyl groups and having a molecular weight of from 62 to 6000, after which the resulting reaction mixture is poured into molds, hardened therein and subsequently removed therefrom. Reference is made to the use of inorganic fillers or even organic fillers, for example in the form of styrene/acrylonitrile-grafted polyethers or polyhydrazodicarbonamide dispersions in polyethers for improving the mechanical properties. The use of the diphenyl methane diisocyanate isomer mixtures even enables casting to be carried out by high-pressure machines because the viscosity of the prepolymer is reduced. However, the components are not selected in such a way that they can be metered solely at room temperature or temperatures below room temperature, for example +10.degree. C., or in such a way that they also represent a cold-hardening, non-shrinking system.
U.S. Pat. No. 3,723,163 describes a process for sealing concrete (steel-reinforced concrete) against existing cracks or developing cracks. In this process, an elastic, adhering intermediate layer of a moisture-hardening NCO-prepolymer is applied to the concrete, followed by the application of a harder, wear-resistant polyurethane layer. Each of the layers may contain further polymers, such as styrene, indene resins, tar or the like. This multistage process is time-consuming, complicated and dependent on weather conditions.
DE-A No. 2,051,946 describes the use of bitumen-containing, filler-containing, polyurethane-forming, cold-hardening components for casting or spraying onto substrates, including substrates of concrete. Unfortunately, the mixtures in question do not show the particular processibility in liquid form of the starting materials coupled with rapid hardening, even on vertical surfaces, or their favorable elasticity and hydrolysis properties.
By contrast, the use of the components discovered in accordance with the invention provides for the machine processing of exclusively low-viscosity liquid components at room temperature or even at temperatures below room temperature, such as are encountered on building sites for example, for very rapid gelation of the polyurethane-forming mixture (so that even vertical surfaces can be evenly sprayed), for rapid, cold-hardening (i.e. at normal room or air temperatures) polyurethane formation which takes place in the complete or substantially complete absence of shrinkage and eliminates the need for highly activating tin catalysts (which on the other hand adversely affect aging behavior). The materials according to the invention give high-strength, abrasion-resistant and hydrolysis-resistant polyurethanes which are elastic, even at low temperatures, and which, by virtue of their crack-free, contraction-free and shrinkage-free formation, are eminently suitable for the corrosion-inhibiting, wear-resistant coating of metal surfaces and moldings (for example interior tube linings) and for the elastic coating of screed, (steel-reinforced) concrete and stone. The polyurethane composition according to the invention also bonds very firmly to existing coatings and may be used in multilayer spraying processes. According to the invention, the layers may even be applied in a fairly considerable thickness because the claimed solvent-free composition gels in fractions of a second to only a few seconds after application and may be processed not only on inclined or vertical surfaces, but even overhead. Using rotating mixing heads, it is even possible for example to line the interior of already laid tubes. The polyurethane bonds very firmly to the substrate. The seal is seamless and even covers over cracks subsequently developing in the substrate, thus preventing the escape of such harmful liquids as water, salt solutions or the like. Thus, the process according to the invention is eminently suitable and more favorable than other coating systems for sealing against the effects of moisture, frost and salts formed by condensation in civil engineering structures.